1) check the rubber seals around the tail lights and 3rd brake light, failing that, your sealing frame around the rear of the top could be leaking. That happens when top shops do a sloppy job fitting a replacement top.
2) at the top of the windshield A pillars, look at the weatherstripping. You will see a triangular shaped outline on the rubber. Over time as the original adhesives in there dry up, water can get in the weep hole then drip out along that outline from inside the weatherstripping. To solve the problem, get some black silicone and smear some over that triangular outline so it seals it up.
3) If you mean the shifter knob, they are available at the dealership, or getbmwparts.com : 25161422879 price is $131.00